An exhilarating blow-dry, or a heavy, pointless waste of an M car? Paul Horrell reports

Time for the convertible already?

Yup, the M3 sedan and M4 Coupe are barely off the starting blocks and here comes the M4 Convertible. As sure as night follows day, the M4 Gran Coupe can't be far away. As for an M3 Gran Turismo, we'd say less likely. Much less.

Well, in most departments other than the obvious capability to give you a 250km/h blow-dry, it's like an M4. Or and M3.

Recap please.

It's driven by a drastically capable straight-six engine with two turbos and anti-lag. An engine that fires the car forward on a perfectly controllable hurricane at pretty well any point on the rev dial. But it's an engine that although loud, doesn't have the bewitching sound or - not quite - the chef's-knife throttle response of its predecessors.

Of course in the convertible, you can take the roof down and get a bigger ear-canal load of its four tailpipes, which adds to the atmosphere. Or you can raise the well-insulated rigid roof, switch the powertrain button to a more civilised mode which closes the exhaust flaps, and use the M4 as a surprisingly civil yet rapid tourer.

But isn't it the handling that undermines chop-tops?

Usually it is. But the M4 Convertible has - just as the hard-top M4 and M3 have - a LOT of extra bracing in the engine bay and subframes to ensure that the wheels are always pointing in precisely controlled directions, untroubled by any bending. BMW M engineers say it's bending that compromises the feel and precision of a car. Torsional (twisting) flex, which most convertibles suffer from, is uncomfortable and a bit disheartening, but it doesn't actually spoil the handling.

So it proves: the M4 Convertible does twist and shimmy a bit when you drop the roof, betrayed by the steering wheel shaking in your hands, but the handling precision doesn't noticeably change.

Surely an M car has to be brilliant at corners?

Well, it's vastly grippy, and possessed of a quick-witted and confident front end. But it's a bit snappy at the back. We found the same in an M4 Coupe on our Speed Week travels recently. If you have the space to do big oversteer, it's good at it. But the zone where confident grip gives way to traction loss is a bit jittery and unpredictable. It gives the traction control quite a busy time of it.

I assume there's a weight issue.

Correct. It's an extra 250kg. Partly that's because the coupe has a carbonfibre roof and bootlid, and here they're steel. Then there's the extra body stiffening for the open car, shared with the regular 4-series Convertible. Then there's the multi-part origami roof itself, and all the fairground-ride of arms and hinges and motors needed to drive it. Secrets of the M4 Convertible's roof here.

Does the extra weight make much difference?

Naturally it marginally deprives you of acceleration, and costs fuel consumption, but you probably wouldn't notice except if you'd stepped right out of the coupe. The weight bias is also some way rearward, so it doesn't have the same balance on a racetrack. I didn't put that to the test, and the car's chief engineer said he doesn't expect anyone will. Owners of M3s and M4 coupes might go on the odd track day, but not convertible buyers. So he said the M4 Convertible has been set up for a slightly softer road ride.

In that respect it's surprisingly supple for a car of its cornering ability, though you can't rely on the adaptive dampers to do enough adapting. If you want comfort you need to switch to 'comfort', but that mode allows too much vertical bounce when you're clipping along, so then you have to switch to 'sport'.

So all-in, does it add to the M4 experience or compromise it?

Both. If you think an M4 should be a hardcore warrior, you won't like the Convertible's extra weight and compromised performance.

On the other hand, you might think - and we do - that the new-generation turbo M car is a different proposition, a faster but less vivid device. In which case maybe Converting it, and adding an extra string to its bow, isn't a bad idea.

Author: TopGear

Top Gear is a British television series about motor vehicles, primarily cars, and is the most widely watched factual television programme in the world.